We’ve known, for some time now, of Microsoft’s plans to narrow the gap that exists between its smartphone and PC apps. Indeed, there has been considerable speculation across the web in recent weeks and months about just how the company intends to implement this, particularly with rumours swirling about plans to consolidate Windows Phone and Windows RT into a single OS in the near future.

The slide above clearly refers to ‘Universal Store apps’, signposting the ability for developers to “create a single app that targets Windows Phone and Windows”. It also describes some elements of the development process going forward, referring to two separate Visual Studio UI projects – one for each of the subtly different user interfaces employed on handsets and larger displays – along with a single “shared solution” template.

A second slide points to common UI elements across Windows and Windows Phone and indicates that 80% of XAML can be shared, with no changes at all, in apps developed for the two platforms.

The slide also notes that, when an app’s development is complete, Visual Studio will produce two AppX packages – one for the Windows Store, and the other for the Windows Phone Store – indicating that Microsoft will ditch XAP packaging in favour of AppX for its smartphone apps with Windows Phone 8.1, bringing it further in line with Windows 8.x.

These latest leaks appear to confirm that Windows Phone 8.1 will be a hugely significant step towards a unified app ecosystem across Microsoft's platforms, with the ability to run near-identical apps both on Windows PCs and handsets marking a major milestone in the journey towards ever-closer OS integration. There remains much that we don't yet know, of course, but given how much info keeps on dripping forth of late, there's a good chance we'll know a lot more before Microsoft officially reveals Windows Phone 8.1 at its BUILD conference in April.